The present invention relates to a current sensor equipped with a Hall element or device.
Current sensors for detecting DC (direct) currents have been widely used in a variety of fields, such as, home electric appliances (air conditioners, automatic washing machines, sewing machines, etc.), industrial equipment and transportation equipment (automobiles, railcars, vessels, etc.).
There is a strong demand for current sensors that are inexpensive but can accurately detect currents in a wide range of temperature.
For such purposes, most current sensors are usually equipped with Hall elements or MR (magnetoresistive) elements for detecting currents. Hall elements are more popular than MR elements for cost performance.
Current sensors equipped with Hall elements are, however, prone to errors caused by change in sensitivity in accordance with change in temperature due to peculiar characteristics of each Hall element.
Moreover, these current sensors suffer generation of an offset voltage (corresponding to a residual Hall voltage multiplied by an amplifier gain) even if no current is detected. The offset voltage depends on variation in the characteristics of each Hall element, temperature change, etc.
There are several types of current sensors having circuitry for canceling the offset voltage.
The inventor of the present invention disclosed one of such types of current sensors in Japanese Un-examined Patent publication No. 2003-14788.
The current sensor is equipped with a Hall element, a differential amplifier and a compensation differential amplifier.
A voltage drop across the internal resistance of the Hall element, which varies in accordance with change in temperature, is supplied to the compensation differential amplifier. The voltage drop is multiplied by a compensation gain p and then output from the compensation differential amplifier. The output is subtracted from the output of the differential amplifier, thus a current-sensor output voltage being produced.
The cost performance of this current sensor is, however, relatively low, because the sensor requires the differential amplifier and the compensation differential amplifier.
There is thus a strong demand for a current sensor that can cancel the drift of offset voltage caused by temperature change with simple and low-cost circuit configuration.